React
Also written as React.js, ReactJS
A popular JavaScript library (from Meta) for building user interfaces out of reusable 'components.'
Think of it like
Like building a house out of pre-fabricated rooms you can snap together and reuse, instead of laying every brick from scratch each time.
Junior or senior?
Junior sounds like
Can build components but struggles to explain the difference between state and props.
Senior sounds like
Can explain that distinction clearly and describe a real state-management bug it caused.
Ask them
“What's the difference between state and props, and when have state management issues bitten you?”
Sounds like real experience
Describes a specific state-management bug — unnecessary re-renders, stale closures, prop-drilling that got out of hand — and the actual fix, not just the state/props definition.
Probe further if
Can define state versus props correctly but has no real bug or refactor story — the kind of gap that shows tutorial-level familiarity rather than production experience.